THIS invention relates to a grout composition.
Matpacks are used underground in mines to provide support for a hanging wall above a footwall. Generally, the upper surface of the matpack is rarely perfectly flat and the hanging wall is usually extremely rough. To ensure that the load imposed by the hanging wall is evenly distributed over the upper surface of the matpack, it is known to provide a flat, flexible bag which is interposed between the matpack and the hanging wall. The bag is pumped up to a substantial pressure with a settable material. Prior to setting of the contents, the flexibility of the bag enables it to take up the shape of the matpack and of the hanging wall such that, when the contents of the bag set, it is in a condition ready to accept the load imposed thereon by the hanging wall and to distribute that load evenly to the underlying matpack. Matpacks are commonly used but an elongate prop having a headboard at an operatively upper end thereof may also be used. These flexible bags are commonly called pack setting bags or prop setting bags and for the purposes of this specification they will be referred to as pack setting bags.
The grout composition which is used in these pack setting bags should fulfill certain functional requirements to be of use in underground mines. As a guide, the grout composition should attain slab compressive strengths of 0.5 MPa after two hours, 2.5 MPa after twenty four hours and 3.5 MPa after three days. The reason for the two hour functional requirement is that subsequent blasting operations usually take place around the area of the matpack and pack setting bag after about two hours and the grout composition in the pack setting bag should be able to withstand any deformation caused by such subsequent blasting operations. Therefore, the grout composition needs to set relatively rapidly. On the other hand, a grout composition which flash sets is not desirable. The reason for this is that the grout composition when mixed with water is typically in the form of a slurry which is pumped into the pack setting bags. This pumping operation of the wet grout composition would not be possible if the dry grout composition flash sets after mixing it with water.
Conventional grout compositions are comprised essentially of high alumina cement. One of the disadvantages with such compositions is that high alumina cement is generally an expensive cement relative to other types of cement. Further, conventional grout compositions do not always give the desired setting characteristics required in practice.
The present invention seeks to provide an alternative grout composition which may for example be used in pack setting bags.